Artificial resins and artificial shellac. simple recipes

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FACTORY TECHNOLOGIES AT HOME - SIMPLE RECIPES
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Artificial resins and artificial shellac. Simple recipes and tips

Factory technologies - simple recipes

Directory / Factory technology at home - simple recipes

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Various natural resins are widely used in the paint industry. Since the source of their production is gradually decreasing, they become technically inaccessible products. This circumstance caused the emergence of a new branch in the chemical industry, namely the production of synthetic resins.

The production of the latter includes obtaining artificial shellacs or novolaks, as they are also called. The production of these products is based mainly on the condensation of phenol and its derivatives with formaldehyde or other aldehydes.

Reaction products of phenol with formaldehyde

It has long been known that the interaction (condensation) of formaldehyde with phenols produces various resinous compounds. These resins, depending on the reaction conditions, the quantitative ratio of the products taken, as well as the composition of the condensing substance (catalyst), have different physical and chemical properties. Some of them are fusible and easily dissolve in alcohol, acetone, an aqueous solution of caustic soda, etc. and are used as novolacs or artificial shellacs. Others are insoluble, infusible and serve as an ornamental material for various purposes (bakelite, rubberite, etc.).

Main raw materials

Phenol, or carbolic acid, found in coal tar, is a brown oil with a very pungent odor. Pure phenol is a crystalline mass with a melting point of 45,5 °C and a boiling point of 182,9 °C. Artificial resin

Cresol - methylphenols C6H4CH3OH - is found in coal and lignite tar. There are three isomeric forms of cresols: ortho-cresol, para-cresol and meta-cresol.

Orthocresol forms colorless crystals and has a phenolic odor. Melting point - 31 °C; boiling point - 188 °C.

Formaldehyde is a colorless, caustic, water-soluble gas formed by the oxidation of methyl alcohol. It is commercially found in the form of formaldehyde, which is a solution of formaldehyde in water and usually contains 40% of the latter. Recent studies have shown that instead of phenol and cresols, derivatives of these substances can also be taken. Instead of formaldehyde - other aldehydes, as well as ketones.

Condensing agents or catalysts

Condensing agents act as catalysts, i.e. take only a temporary part in the reaction. Once the reaction is complete, these substances are sometimes removed from the resulting product. There are acidic and basic catalysts. Acid agents include acids, acid salts, and in general any salts that can produce an acidic reaction upon hydrolysis. Ammonium chloride (ammonia) is an acid catalyst, since when it is exposed to formaldehyde, hydrochloric acid is released.

Alkaline agents include alkalis and alkaline-reactive salts, as well as salts that, upon hydrolysis, are split into a weak acid and a strong base. According to Bakeland's research, acid catalysts promote the formation of shellacs, while alkalis produce predominantly Bakelite-type resins.

The process of obtaining shellac

To obtain shellac resin take:

Phenol 50 wt. hours;
Formaldehyde from 40 to 60 wt. hours;
Hydrochloric acid from 1 to 5 wt. h.

All components are placed in a vessel of a suitable size. With a sufficient amount of condensing substances, the reaction can begin at ordinary temperature, and the liquid mixture is divided into two layers: one watery layer, consisting of separated water and water-soluble substances, and an oily layer containing the initial condensation products. In practice, to speed up the reaction, the mixture is heated slightly.

To avoid loss of volatile components from the mixture, heating is carried out in a closed vessel equipped with a reverse refrigerator, i.e., the vapors, rising up the tube, are cooled by water and, condensing into liquid, flow back into the reaction boiler.

As it heats up, the viscosity of the oil layer increases. Heating is stopped when a thick consistency is reached. The oily mass can be separated from the aqueous layer, or the whole can be evaporated until the mass is solid at ordinary temperature, and therefore there is no need to separate the layers. The mass obtained in this way is colorless or yellow-colored, melts, easily breaks down and is soluble in alcohol, acetone, phenol and sodium hydroxide solution.

production method

According to this method, artificial shellac is prepared as follows:

Mix 10 wt. parts ortho-cresol, 7 wt. parts of commercial formaldehyde (contains 40% formaldehyde), 10 wt. hours of water and add 0,4 wt. including strong hydrochloric acid. The resulting mixture is heated for several hours with constant stirring. The resulting resinous product is separated from the watery part and washed with hot water or prolonged exposure to steam.

The resin thus obtained is colored from yellow to light brown, easily soluble in methyl alcohol, acetone, carbon disulfide, ether, chloroform, etc.; soluble in dilute alkalis, more difficult to dissolve in benzene and terpineol; insoluble in turpentine, fatty acids and oils. Varnishes prepared on artificial shellac provide a quick-drying, very shiny surface.

The following method aims to obtain condensation products of phenol or its homologues with aldehydes and use these products for the manufacture of varnishes.

When cresols are condensed with formaldehyde in the presence of alkalis, products are obtained that are soluble only in alcohol and therefore cannot be mixed, for example, with resins that are insoluble in alcohol. Their alcohol solutions can serve as varnishes for coating metals when heated, but they are not suitable for coating elastic objects, such as fiber, thin iron, tarpaulin, cardboard, etc. If condensation is carried out in the presence of lead acetate salt, then a product is obtained that is soluble in alcohol and benzene, miscible with ordinary resins and giving hard, elastic coatings when heated.

Example:

Cresolic acid 100 wt. hours;
Formalin 40% 130 wt. hours;
Acetic lead salt 15 wt. h.

Heat everything to a boil in a vessel with a refrigerator; after the moment of condensation occurs (a thick, hardening mass), the heating is stopped, the varnish is separated from the water layer and boiled to the desired thickness.

Author: Korolev V.A.

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